In recent years, catheters have been being used in an increasing number of diagnostic and/or therapeutic methods for alleviating the physical and time-basis burdens on patients. Generally, for insertion of a catheter into a living body through a blood vessel, ureter, trachea, esophagus or the like and bringing the catheter accurately to a predetermined site in the living body without damaging the blood vessel wall, organs or the like, the catheter must meet the structural requirements for high operationality and safety when serving as a medical device and, simultaneously, the luminal internal surface of its tube (referred to also as “catheter body”) must exhibit lubricity.
The lubricity is necessary for externally injecting a liquid medicine or the like to a predetermined site in the patient's body through the lumen of the catheter body, for draining a body fluid in the living body or the like, or for passing other therapeutic device therethrough.
As a catheter which meets such structural requirements and further has lubricity at the luminal internal surface of a catheter body, for example Patent Document 1 describes a catheter including a catheter body having an outer layer and an inner layer, the outer layer having a first region and a second region located on the proximal end side of the first region, wherein the first region is composed of a polyester elastomer, and the second region is composed of a polyurethane elastomer higher in hardness than the polyester elastomer constituting the first region. This catheter is excellent in operationality such as pushability, torque transmitting property, following property, and anti-kinking property. Besides, in the catheter, a material capable of reducing the friction of an internal surface of the inner layer, for example, a fluorinated resin such as polytetrafluoroethylene (PTFE) is used as the material constituting the inner layer, so that the luminal internal surface of the catheter body has lubricity.
There are many examples in which a fluorinated resin, particularly, PTFE is thus used as the material constituting the luminal internal surface of the catheter body.
Meanwhile, a catheter must be sterilized before used, since it is used for a living body, like other medical devices. General sterilization methods include the methods in which a gas or water vapor is used. These methods, however, have problems as to the toxicity of the gas, the long treatment time required for sterilization, etc.
In view of these problems, the sterilizing method using radioactive rays such as electron beams have come to be paid attention to. According to this method, toxicity is obviated and the treatment time required for sterilization is short.
However, the sterilization method using radioactive rays cannot be applied to the above-mentioned catheters using PTFE.
This is because PTFE is deteriorated when irradiated with ionizing radiations of not less than 1 kGy, and is extremely deteriorated in mechanical properties at an absorbed dose of around 25 kGy, which is a sterilizing dose generally used in the cases of sterilization with γ-rays, electron beams and the like.
For example, when the radioactive-ray sterilization is applied to the catheter described in Patent Document 1 in which PTFE is used to form the inner layer, PTFE is conspicuously lowered in breaking elongation and, therefore, mere bending of the catheter body would result in exfoliation or cracking of the inner layer.    Patent Document 1: Japanese Patent Laid-open No. 2001-190681
Disclosed here is a process for producing a catheter that includes a catheter layer having a luminal internal surface consisting of a material that has lubricity substantially identical with that of PTFE and has a resistance to radioactive rays not had by PTFE.
A process for producing a catheter as disclosed here involves mixing ETFE and PTFE in a mass ratio of from 99:1 to 45:55 and forming the mixture into a tubular body, forming a reinforcement layer and a resin layer on the tubular body obtained and forming a catheter, sealingly packaging the catheter, and sterilizing the packaged catheter with radioactive rays.
The luminal internal surface of the catheter disclosed here has a lubrication characteristic substantially identical with that of PTFE. Therefore, the use of the catheter makes it possible to easily carry out injection externally a liquid medicine or the like to a predetermined site in a patient's body through the lumen of the catheter body, drainage of a body fluid or the like present in the living body, and passage of other therapeutic devices therethrough. In addition, the luminal internal surface of the catheter is composed of a material having a resistance to radioactive rays not had by PTFE. Therefore, a sterilizing method using radioactive rays, which obviates toxicity and ensures that the treatment time required for sterilization is short, can be applied to the catheter disclosed here.